Abstract 1054: S100B affects cell signaling in malignant melanoma

Abstract

Abstract Establishing the mechanism by which S100B effects ERK and its downstream proteins will provide valuable insight into the role of S100B in the progression of melanoma and potentially aid in developing new pharmacological drugs. S100B is a 21.5 kDa symmetric homodimer that is highly conserved and expressed in a number of tissues and cell lines, including melanocytes. Generally, low levels of S100B have trophic effects, while higher levels are problematic, as is the case in human malignant melanoma. S100B is an effective and widely used prognostic marker for malignant melanoma, with increased levels of serum S100B being predictive of disease stage, increased recurrence, and low overall survival. It has previously been found that S100B directly interacts with the tumor suppressor protein p53, down-regulating its protein levels, thereby allowing damaged cells to proliferate and mutations to propagate. S100B has also been implicated in several other signaling pathways, including the MAPK pathway (BRAF-MEK-ERK). The initial hypothesis tested was that S100B inhibits the phosphorylation of ERK targets in a calcium-dependent manner. To evaluate the significance of S100B in melanoma cell lines, stable S100B knock-down clones were created using lentiviral shRNA particles. The extent of the knock-down varies among the clones and shows a correlation between the level of remaining S100B and the level of phosphorylated ERK, where the clone with the least amount of S100B also has the lowest level of phosphorylated ERK. The clones also display a decreased rate of proliferation measured with both an MTT based assay, as well as with electrical impedance. Over-expression studies were also conducted where normal human S100B, but not a mutant S100B incapable of binding calcium, results in increased phosphorylated ERK, but decreased phosphorylated RSK at Thr573. To determine if S100B was interacting with RSK directly, pull-down assays were performed, and RSK was detected in S100B pull-downs in the presence of calcium; however, it was not detected in the presence of the calcium chelator EDTA. In conclusion, we demonstrate that the calcium-binding protein S100B affects the MAPK pathway by simultaneously increasing phosphorylated ERK and decreasing phosphorylated RSK, together which are consistent with the increased growth rates and cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1054. doi:10.1158/1538-7445.AM2011-1054